The present invention relates to speech recognition for recognizing a speech uttered as one of a plurality of stored reference patterns and, in particular, to a speech recognition method and system for reducing the noise accompanying the speech uttered.
In a known speech recognition system, a speech uttered is converted into an input speech signal by an electromechanical transducer such as a microphone. The input speech signal is analyzed by a pattern analyzer and is converted into a digital input pattern signal. The input pattern signal is memorized in an input memory as a memorized pattern. The memorized pattern is compared with each of the stored reference patterns in a reference memory and a dissimilarity is produced therebetween. When a particular one of the reference patterns provides the minimum dissimilarity, the speech uttered is recognized as that particular reference pattern. Alternatively, when a specific one of the reference patterns provides a specific dissimilarity smaller than a predetermined threshold value, the speech uttered is recognized as the specific reference pattern.
In actual recognition operation, the input speech signal is accompanied with noise due to presence of background sounds. The input speech signal and the noise are collectively referred to as an input sound signal. Accordingly, the input pattern signal includes a noise component. This result, in a worst case, in a failure of the speech recognition operation.